How many cells are in that?
The lungs have the surface area of half a tennis court, folded into a chest cavity. The gut is bigger still.
Almost exactly a cells in the body
37,000,000,000,000 cells is more than 3 of the 6 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| neurons in the brain | 86,000,000,000 cells | 430× | |
| cells replaced per day | 330,000,000,000 cells | 112× | |
| red blood cells | 25,000,000,000,000 cells | 1.48× | |
| cells in the body | 37,000,000,000,000 cells | 1× | |
| bacteria in the body | 38,000,000,000,000 cells | 0.974× | About one per human cell |
| synapses in the brain | 100,000,000,000,000 cells | 0.37× |
Worth knowing
- The body contains roughly 37 trillion human cells and about the same number of bacteria — the old "ten to one" ratio was an error repeated for forty years.
- You replace about 330 billion cells a day, roughly 1% of yourself, mostly gut lining and blood.
Frequently asked
How many cells are in the human body?
About 37.2 trillion by the most careful estimate, of which 84% are red blood cells by count but only a few percent by mass.
How much surface area do the lungs have?
About 70 m² — half a tennis court — from roughly 480 million alveoli, each about a fifth of a millimetre across.